US2568779A - Multiplex system for telegraphic and radiotelegraphic transmission with decametric waves - Google Patents

Description

Sept. 25, 1951 H. M. VEAUX ,77

MULTIPLEX SYSTEM FOR TELEGRAPHIC AND RADIOTELEGRAPHIC TRANSMISSION WITH DECAMETRIC WAVES Filed Aug. 13, 1948 2 Sheets-Sheet 1 vamcnz.

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. INVE NTOR HEN/Pl Mfll/IP/CE VZHUX ATTORNEY Sept. 25, 1951 H. M. VEAUX 2,568,779

' MULTIPLEX SYSTEM FOR TELEGRAPHIC AND RADIOTELEGRAPHIC TRANSMISSION WITH DECAMETRIC WAVES Fil ed Aug. 15, 1948 2 Sheets-Sheet 2 ATTORNE Y Patented Sept. 25, 195 1 MULTIPLEX SYSTEM FOR TELEGRAPHIC AND RADIOTELEGRAPHIC TRANSMIS- SION WITH DECAMETRIU WAVES Henri Maurice Veaux, Saint-Lcu-la-Foret, France Application August 1948, Serial No. 44,195 In France August 14, 1947 This invention relates to a multiplex high speed telegraph system with time distribution allowing I low rate (teleprinters for instance), presents a great flexibility in operation by adapting itself by an easyadjustment to the variable conditions of propagation, and to its use in wire transmissions;

It is well known that in a long distance radio electric transmission by decametric waves, the signals arrive at the receiving station by paths having different lengths. The transmission of'a short pulse gives at the receiving end a train of pulses producing the well known reverberation phenomenon. The same propagation mechanism explains the Well known phenomenon called selective fading in radio t lephony; the experimental results show that on a Europe-U. S. link the difference in time for the two shortest paths is in the order of l'millisecond. It is known also that a train of short pulses transmitted at regularly spaced intervals, the duration of which is greater than the reverberation time, does not produce, at the receiving end, heads of signals succeeding according to the same order of regularity, and this is explained by the changes be tween two successive pulses of the propagation 30 conditions on the shortest path.

The present invention is based on the following principles:

(1) If a train of signals is transmitted with a duration of less than the difference in thetravel' times 01 along the two shortest paths (that is, 1 millisecond in the above mentioned example), a true reproduction ofthe signals is obtained at the receiving end by receiving the only train arriving first along the shortest path: the transmission must be effected discontinuously by successive trains having a duration less than 01, spaced apart by time intervals corresponding atthe re-" ceiving end to the reverberation signals which are not required;

(2) The first train gives a true reproduction of the signals particularly as concerns the phase relations; the time interval At separating two signals of the same train tends to be maintained durf ing the propagation when At becomes veryshort;

the transmitting frequency thus offers substantially only slight changes due to the propagation.

In radio telegraphy however, the practical realisation is simplified because it is not necessaryto efiect'the storage of the signals for transmission with a duration conversion at the-transmitting 4 Claims. (Cl. 2509) end followed by a reverse duration conversion at multiplex radio telegraphic high speed systems comprising several channels exploited for instance, by teleprinters; such systems which are relatively simple suppress in practice the reverberation and echo effects and give a very efiicient protection against interference; they adapt themselves with the desired flexibility to the variable conditions of the propagation and to the wire transmission.

The invention consists in the provision of such systems wherein each train comprises reference elements for amplitude or phase; it allows the method of telegraphy used in UHF transmission to be applied to the decametricwaves transmission by limiting the transmission to discontinuous trains separated by times allotted to the reverberation effects which do not exist in UHF constituents.

In a first system the transmitting telegraphdevices (teleprinters for instance) are assembled inn identical groups comprising each N devices; during a time equal to the telegraphic time identical for the various channels, the Nn channels are scanned in periods of equal duration 01 separated by free intervals, the scanning by the train corresponding to a group; the scanning duration 91 of one group is less than the time interval (1 millisecond for instance) which separates the arrival at the receiving end of a same signal transmitted along the two shortest paths and the duration 02 which separates the end of the scanning of a group from the beginning of the scanning of the following group is greater than the practical reverberation time; at the receiving end, the signals of a same train arriving along the shortest path are collected and transfered to the corresponding telegraph receivers; the duration of a telegraphic time identical for the various channels (i. e. 20 milliseconds for a teleprinter) represents the sum of the scanning times for the a A more thorough understanding of the present invention may be had from the following detailed description and the accompanying drawings, in which Figures 1, 4 and 6 are schematic diagrams of an embodiment of my invention; Figure 2 is a diagrammatic representation of the scanning sequence used and Figures 3, and 7 are graphical aids to the understanding of the operation of the invention.

The following embodiment given as illustration will eliminate all doubt as to the object of the invention: The system shown in Fig. 1 for the transmission, and Fig. 6 for the reception, corresponds to a transmission comprising 16 teleprinters having a transmission speed normalised to 50 bauds; the scanning of a telegraphic time on the 16 channels is made, asis well known,- by interleaving in a time equal to 20 milliseconds; for the scanning the teleprinters are dis- 7 tributed into four groupsiof four devices accordingto Fig. 1. The various groupscomprise the teleprinters (T2, T3, T4, T5) (T1, T8, T9, TIE) (TIZ, Tl3, TI i, TI5) (TII,'TI$,ITI9, T); in

normal operation, sources TI, T6, TI! and Tit,

produce synchronising signals used as reference signals in the transmission of a signal time. The

beam F of an electronic switch T sweeps according to the method well known in television (Fig...

travel times along the two shortest pathspthe time 02 from the end of a swept line to the origin of the next line as well as the time of transit from contact 29 to contact I being greater than the practical reverberation time. The passing of the beam F on the four contacts of a same line following the first one (i. e. 2 to 5 for the first line) successively unblocks the amplifiers A2 to A5, which are fed by the teleprinters T2 to T5. Fig. 1 shows only a part of the teleprinters distributed into four groups GI, G2, G3 and=G i. The amplifiers fed by the teleprinters have ia common output Si from which a signal regenera' tor R is fed, this regenerator being of a known type in interleaved scanning; said regenerato'r" gives at its output a signal continuity at the arrival of two successive marking pulses from 2 successive channels, the return-to rest resulting from a space or from the end of a line scanning. In the case of the end of a line, the control of R for return to rest may be effected by sweeping of a supplementary brush, the sweeping time of which is comprised in the time 02 imposed by the reverberation effect. synchronising signals obtained at S2 are intermixed with the signals from R to give at S the current used for the electronic keying of the transmitter. The sweeping movement of F is effected according to the method conventionally used in television; the synchronism and the local phasing of the driving heads of the transmitter using perforated tapes and of the movement of F, give the interwoven scanning of the various channels: for this purpose, according to a well known method, a basic oscillator 0 gives after the required frequency changes the sawtooth potentials applied to V and H, the vertical and horizontal deflection condensers for the beam The 7 F. The same oscillator feeds the motors of the driving heads of the transmitters. For a tele graphic speed of bauds (telegraphic time T=20 milliseconds) and a reverberation having a duration 02:4 milliseconds, the sweeping movement of F corresponds to a duration 01:1 millisecond for the scanning of a line, the return to the beginning of the following line being efiected in a time 02:4 milliseconds. The keying speed of the signal at S is in the order of 5000 bauds; the image and line frequencies are equal to 50 and 200 respectively.

The sweeping potentials for images and lines (Fig. 3) are obtained in accordance with the known methods. The direction of the movement oi-sweeping of thelines may differ from that normally used in television.

One of the conventional systems for producing the saw-tooth signal shown in Fig. 4 gives the desired results: the pulses acting on the grids spaced at intervals of 5 milliseconds fromthe oscillator 0 determine the instants of the charge of 0 through R2, and thebeginnings of the periods 01 of line sweeping, whilst the charge times through'RI correspond toti'mes '02 (Fig. 5). Since the time (014-02) is' maintained constant at 5 milliseconds for instance, the duration 01 of aline sweeping is determined by adjusting R2; it is thus easy to adjust 01 from a low value to 5 milliseconds, the

latter corresponding to the practical absence of. reverberation. This adjustment of 01 does not change the operation of the telegraphic transmitters, and may be effected at the request of the receiving operator according to the. propagatband occupied .by the multiple transmission (transmission speeds equal to 1000 bauds in the Moreover, the same.

absence of reverberation). apparatus may be used as well for transmission bywire. in which case 02=0-as well as for radioelec'tric transmission by a simple adjustment of 01. The. line sweeping, may be effected alon horizontal lines by the use at point V of a I (Fig. 2) which is different from those from thesynchronising contacts 6, II and I6, may be s'imultaneously'used as image and line signal; a

v T, movement synchronised with that ofbeam F; during-this movementv the beam .unblo'cks the 16 amplifiers a2, a20 of the 16 channels;. thepulses from these amplifiers produce according to known methods the regeneration of the telegraphic signals (regeneratorsmZ to which' difference in the lengths of the contacts controls the relative duration of the signals. Fig. 6 gives a schematic layout of the receiving system; the

signals from receiver 1* are separatedgthe syn-- chronisin'g signals selectedat s control. thesaw- 1 tooth potentials which, collected-ate and ,h and applied to the vertical and horizontal deflection condensers,.produce the sweeping whosefmovee ment is of the beam F of an electronic switch feed the receiving teleprinters i132 to-t29.

The advantages of the system are-as follows:

(-1) Radioelectric advantages: thereverbera tion effects do not exist: the influence of the; echoesmay be suppressed: 02 may in any case be I ga iustsd t t the enres sm te-be ween its 1 useful signal trains; finally the influence of the statics is reduced since the time 01 attributed for the reception is relatively short; the bias of the input tube of the receiver may further be controlled by the line synchronizing signals in such away that the receiver be in receptive condition only during the times 01' necessary for receiving the useful signal trains.

(2) Flexibility of use: 'Since the telegraphic time T'=n(a1+02) is constant, it'is easy to ad-' just the time '01 according to the propagation conditions and to employ the same apparatus on wirelinksif02=0; 4

Likewise it is possible to set according to the' propagation and interference conditions the number N of apparatus'of a same line by simply adjusting the amplitudes of the horizontal 'deflection of the beam F and F; an amplitude giv ing asweeping of the contacts I to 3 (Fig. 2) corresponds to two channels used by line; for the purpose of facllitatingthe settings at the "transmitting and receiving ends, it is necessary to'use a visual supervision constituted for instance by a cathode ray tube (not shown) arranged in par-. allel with the tubes T or T and the spot of which is displaced according to a pattern reproducing the contacts I to the coincidence of the scanning spot on the contact lines, the number of which is easily chosen, is thus obtained.

In practice, the propagation conditions on the shortest path do not present any substantial change during the 4 50 second corresponding to the sweeping of an image; a single synchronising signal for each image is then necessary; only contact I may be used for the synchronisation; the corresponding pulse is used at the receiving end for synchronising a stable oscillator placed at s and which gives according to known methods the vertical and horizontal deflection potentials for the beam F; the contacts 6, l l and 16, may be used for different channels; only one synchronising signal for each image is then necessary for 19 channels; a simple switching system enables the passing according to the propagation conditions from the 16 channel arrangement comprising four synchronising signals for each image to the 19 channel arrangement having a single synchronising signal for each image.

The methods of supervision of the probable exactitude of the received signals, particularly by using as well known a 7 unit code, may be adapted to the system of the invention; due to the transmission quality of the system, however, the loss of two units out of 7 represents an unnecessary extravagance, and a less expensive supervision would be sufiicient, said supervision being effected simultaneously on all channels or all the channels of a line and using some determined contacts corresponding to a marking or a spacing: at the receiving end, the absence of a signal on a marking contact or the presence of a signal on a spacing contact, is translated into vague signals, which attracts the attention of the operator; a line supervision may use the contacts simultaneously allotted to the synchronising sig nals (contacts I, 6, ll, l6); if a supervision by channel is desired, the quality of the system enables the use of a 6 unit code. I

The system enables an easy interconnection between a transmission network using underground or radio cables and a radio network using decametric waves, the discontinuous transmission decametric wave group being capable of occupying a part of the time of the continuous transmission effected on underground or radio cables.

-The' number of channels may be increased by changing the carrier frequency at the end of the transmission of a train occupying a line; in the above mentioned embodiment comprising a line scanning of 1' millisecond and reverberation of 4 milliseconds four five-contact lines-may be inserted between two successive contact lines of Fig. 2: the complete contact pattern thus presents 20 lines which are continuously swept, the passage from the end of a line to the beginning of the following one being very rapid; this passage is accompanied by a sudden change in the carrier frequency. Then first'lines thus produce the transmission of the 5* trains an millisecond having 5' successive frequencies NI, N2,"N3, N4 and N5, which are sufficiently spaced out for the reverberation effects from one line to the next one to be conveniently separated at the receiving end; The same cycle'of change in the carrier frequencies may be repeated cyclically for each series of 5 lines. A telegraphic keying 'of-the carrier frequency of the transmitter is therefore effected according to a periodic sequence having a period-equal to 5 milliseconds and adaptedto: be controlled from the oscillator 0 (Fig. 1) according to the conventional method of keying by frequency shift. At the'receiving endfthe signals belonging to lines having the same carrier frequency may be separated by frequency selectivity; The signals of all lines may also be translated to a same intermediate frequency by keying the frequency of the frequency shift oscillator in synchronism with the changes effected at'the transmitting end. In radiotelegraphy account may be taken of therapid decrease of the reverberation by using a law of convenient variation of the carrier frequencies comprising diminution of difference from N2 to N5 (Fig.7); the whole frequency difference may thus be substantially reduced without inconvenience; the frequency difference enables the separation at the receiving end of the signals belonging to a line having the same number; there fore are-separation of the channels belonging to a same line is effected. Due to difficulties in the manufacture of a tube having a considerable number of contacts, a group of several tubes may be used, the lines of which are successively swept during a telegraphic time according to well known methods.

Another construction of tubes T or T may be adopted by arranging, in front of the electrodes, a plate provided with an aperture opposite each electrode; this plate has a potential slightly higher than that of the electrodes, when the beam passes through the aperture a secondary emission is produced from the corresponding electrodes, said emission being absorbed by the plate and enabling the channel unblocking pulse to be produced. At the receiving end the signals may be used for the modulation of the electronic beam by receiving the secondary emission pulses corresponding to the marking times on the channel in question on an electrode.

Other ways of using the electrode may be considered, especially the destination of the electrodes of a same line to a same channel with a code of 5 or more units, the differentiation of a character on a channel by the distance separating 2 pulses on a line intended for the said channel, or transposition of the Hughes system of keying. Hughes keying is a directly worked (as opposed to relay worked) synchronous typeprinting telegraph, having a sending keyboard containing black and white keys arranged alt-er-.

nately in similar fashion to a pianoflkeyboard. The position of the key depressed determines the instant at which a current impulse is transmitted. For a full description of Hughes keying reference may be had to the text Telegraphy, written by T. E. Herbert (fourth edition), printed by Pitman and Sons; Ltd, in Chapter XIII thereof entitled, The Hughes. H e

In the case of 2 channels per line,--f or instance, theline comprises 4 contacts, thefirst of which gives the synchronising signal, and the other three enabling the characterisation of the mak condition existing onthe 2 channels. e The invention is not limited to the sweeping by means of parallel straight lines a circular sweeping may be adopted for instance, by the use of a cyclophon tube normally used in UHF transmission, and conventionally employed for discontinuous transmission; It is well known that a cyclophon tube comprises a cathode beam provided with a circular movement, a plate having a number of apertures equal to the number of channels, and electrodes or dynodes, one in front of each aperture; during its rotating movement the beam passes through the aperturesv and strikes the electrodes with a potential less than that of the plate; there then results a secondary emission betweeneach electrode and the plate which gives the unblocking pulse for the channel in a system having the features of the straight sweep system use'may be made of a cyclophon.

What is claimed is:

1. A time multiplex telegraph system comprising a plurality of grouped telegraphic transmitters adapted to transmit make and break signals in different channels, onechannel for each group, a transmission medium common'to all of said transmitters having at least two paths of dilTerent lengths, means for. cyclically scanning said channels, means for recording the, output of said channels during a time interval equal to the time required by said scanning means to scan the said channels, means to group together the make or break signals from said channels, thereby to form trains of grouped signals, the duration of each train being shorter than the difference in the duration of times of travel of said signals over the two shortest paths of said transmission medium, means forseparating said grouped signal trains by a time interval ;equal to the time of travel of reverberated signals through said transmission medium, means coupled tosaid transmission medium -for-receiving said signal trains,- said receiving means comprising means for'cyclicall separating said re ceived signal trainsfa plurality of=means for regenerating said separated received signals; and a plurality of means for translating said regenerated signals, said separating means adjusted to operate only during thetime interval equal to the time of travel of reverberated sig'nals through said transmission medium.- V 2. A time multiplex telegraph system as claimed in claim 1, whereinsaid transmission medium comprises the ether; .saidcyclically scanning means comprises a,cathode-ray tube having ,.a plurality of dynodes, one corresponding to each of said transmitters, said dynodes adapted to be swept by the cathode ray beam of said tube, and

are identical.

means to deflect the cathode ray, beam of said tube. j 3. A time multiplex'telegraph system as claimed in claim 1, wherein said transmission medium comprises a wire link. I

I, 4. A time multiplex telegraph system as claimed in claim 1, wherein the cycles of operationbf said scanning means said separating'means HENRI MAURIQEVEAUX.

REFERENCES CITED The following references are of record in? UNITED. STATES'PATENTS c,

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